Ultrasound technology has been used for therapeutic and diagnostic medical procedures, which can include providing imaging of internal portions of a body. Ultrasound procedures typically use a transducer assembly to emit and/or receive signals. In some cases, a stationary transducer assembly can view a full image area due to the particular positioning of the multiple ultrasound elements in an array. Another design includes a rotating transducer assembly having a single ultrasound element which obtains data by mechanically rotating the transducer assembly. In that case, data are obtained by the transducer assembly emitting sequential ultrasound pulses at changing rotational positions. Advantages of the single-element rotational design when compared to an array design include smaller catheter diameter, better image quality, possible higher center frequency, lower cost for the ultrasound imaging console, and less ring down artifacts (dead zone).
Single element designs can also include certain disadvantages, such as non-uniform rotational distortion (NURD). During imaging procedures including a single element design, the ultrasound element is typically rotated with a torque cable. Ultrasound pulses are emitted in an even-spaced time-sequential manner under the expectation of a uniform rotation rate of the ultrasound element. Each reflected ultrasound pulse or echo signal represents a portion or scan line of an image. An image processor assembles the data based on the assumption that the data points represent images from evenly-spaced pulses. However, it can be difficult to achieve a uniform rotation rate for the ultrasound element when using a torque cable as a driving means. The ultrasound element can be around one meter from the driving end of the torque cable. Ideally, the torque cable will have sufficient stiffness to provide uniform rotation at both ends while simultaneously allowing maneuverability. However, practically a sufficiently maneuverable torque cable creates a potential for delay in the transferring of torque from one end of the cable to the other, as the cable stores and releases elastic energy, which causes the transducer assembly to rotate at a non-uniform rate even when the rotation source rotates at a uniform rate. The non-uniform rotation rate causes the resulting images to be distorted.
Attempts to create single element designs without torque cables present further problems. Designs which include a microminiature motor positioned near a stationary transducer assembly and a rotating reflector require additional space. In addition, control wires or structural components can cross the viewing window causing a portion of an image to be blocked. Another problem is the possibility of breaking a catheter tip which includes the ultrasound transducer. Designs including a microminiature motor positioned near a rotating transducer assembly present further problems. Current commercialized designs use costly and bulky rotary transformers to connect stationary electrical wires from a console to a rotating ultrasound element. However, the rotary transformer is among the most expensive components of such imaging systems. Slip rings have disadvantages in that they take up space and can add electrical noise to the ultrasound signals.
Other problems exist in current designs. Typically, transducer assemblies are positioned in a dedicated catheter. The catheter usually shares the same utility lumen as therapeutic catheters preventing a physician from performing imaging monitoring simultaneously with or during additional procedures, such as, for example, deploying a stent or graft or performing a biopsy.
Thus, there is a need to have an ultrasound system design that could be integrated with a catheter, that is cost effective, small in size, and which produces images free from NURD artifacts and blocked viewing areas.